The invention relates to an apparatus and a method for feeding a through-bolt through coaxially aligned openings through a stator core of a dynamoelectric machine, which openings form a bore through the stator core, while initially feeding the through-bolt towards a first end of the bore along a line forming an acute angle with the axis of the bore.
Large dynamoelectric machines such as generators typically have stator cores, which usually comprise many axially thin annular laminations that are assembled together and compressed to form a cylindrical stator core supported in a frame. Stator coils are received in radial slots in the radially inner periphery of the stator core which extend beyond both axial ends of the stator core and are interconnected to form a stator winding. The stator core laminations have coaxially aligned openings therethrough which form bores through the stator core, and through-bolts extend axially through the bores, with nuts provided on both axial ends of the through-bolts which are torqued or hydraulically tensioned to hold core support system in assembled position and maintain the axial continuity and integrity of the stator core. The throughbolts are insulated, with the nuts maintaining the laminations in axial compression. Such a dynamoelectric machine is described in U.S. Pat. No. 4,227,109, assigned to the assignee of the present invention, and the contents of which are incorporated by reference herein, and which is directed to a system for providing uniform expansion of a stator.
The through-bolts, without the nuts, are generally free to slide axially relative to the frame of the dynamoelectric machine and through the bores in the stator core. These machines, and the through-bolts are large assemblies, with a typical through-bolt being about 3.175 cm (1.25 inches) in diameter wrapped with dielectric insulation to give a total diameter of about 4.29 cm (1.69 inches) and being about 7.62 meters (300 inches) in length, with such bolts weighing on the order of about 45 Kg (100 pounds). At times, the removal of a through-bolt from a stator core is required, such as in retrofitting of the dynamoelectric machine. Often, however, the dynamoelectric machine, because of size, is disposed in a space below the normal floor line of a building, such that the machine is often partially below the floor line. Thus, difficulties often arise due to the lack of clearance available between the end of the stator core and the wall of the foundation or floor level of the building. Such an absence of sufficient clearance prevents the axial alignment for insertion of a through-bolt into the bore of the stator core.
There are currently two known methods in use for the retrofitting of such through-bolts. One method requires that the entire generator and rotor be lifted out of the space below the floor level to allow new bolts to be inserted. This method is very expensive and time consuming. also, when one lifts the generator, one runs the risk of causing misalignment which could cause increased rotor vibration. A second method of installation of a throughbolt requires the use of segmented through-bolts. A segment is partially inserted and then welded to a following segment. The assembly is fed further into the bore and a further segment attached thereto, and the sequence repeated until the attached segments form one long bolt running the length of the generator. Because of the welds, however, such segmented through-bolts are weaker than their one piece counterparts, and are simply too weak for some applications. This procedure also involves the use of a substantial amount of time and expense.
It is an object of the present invention to provide a system that will enable the insertion of a through-bolt through the stator core of a dynamoelectric machine, which is disposed in a recessed space having insufficient clearance for axial aligning of the throughbolt with a bore in the stator core.